Careful and optimal preparation of a hard body tissue such as a portion of bone or tooth to receive an implant is key to a procedure's success. Many factors may affect the strength and overall outcome of the implant's performance, including the acute cleanliness and preparation of the tissue for acute implant fixation strength, as well as any preparation to promote bone healing and remodeling, necessary to promote desired fixation over time.
Wound healing is the body's natural response for repairing and regenerating tissue, which is generally categorized into four stages: 1) clotting/hemostasis stage; 2) inflammatory stage; 3) tissue cell proliferation stage; and 4) tissue cell remodeling or growth stage. In the case of bone, which has the ability to heal and remodel, the natural process starts when the injured bone and surrounding tissues bleed, forming what is often called fracture hematoma. The blood coagulates to form a blood clot situated between broken fragments of a fractured bone, or between an implant surface and bone, in the case of a bone implant procedure. This blood clot serves as a bridge or conduit for the healing and growth cells to travel, so as to preferably fuse pieces of bone, in the case of a fracture, or integrate the implant with the bone, in the case of a bone implant procedure. Within a few days blood vessels grow into the jelly-like matrix of the blood clot. The new blood vessels deliver phagocytes to the area, which gradually remove any non-viable material or debris such as dead or necrotic tissue or bacterial matter, which may otherwise obstruct or delay the wound from healing and bone from remodeling or growing. This clotting of blood activates platelets which in turn cause the release of a multiplicity of growth factors and cytokines, critical to wound healing, as they cause osteogenic cells (bone forming) to migrate to the wound site. The blood vessels also bring fibroblasts in the walls of the vessels and these multiply and produce collagen fibers. In this way the blood clot is replaced by a matrix of collagen.
At this stage, some of the fibroblasts begin to lay down bone matrix (calcium hydroxyapatite) in the form of insoluble crystals. This mineralization of the collagen matrix stiffens it and transforms it into bone that now connects the fractured bone together or the implant component to the bone in the case of an implant. This initial “woven” bone does not have the strong mechanical properties of mature bone. By a process of remodeling, the woven bone is replaced by mature “lamellar” bone. The whole process can take up to 18 months, but in adults the strength of the healing bone is usually 80% of normal by 3 months after the injury.
Bone remodels or grows as a natural reaction to being placed under repeated stress, such as weight bearing exercises. Stress on the bone result in the thickening of bone at the points of maximum stress. It is hypothesized that this is a result of the bone's piezoelectric properties, which cause bone to generate small electrical potentials under stress. This piezoelectrical property has also been used to promote bone growth, by the external application of an electrical field to areas of damaged bone during healing, described in more detail later.
Interruption or failure of the healing process may lead to the failure of the implant to connect (osseointegrate) with the resected bone or the failure of a bone fracture to fuse, and consequently an inferior procedural outcome and/or a possible additional surgery. A number of factors may overwhelm the body's ability to effectively heal a wound and for bone remodeling to occur, such as repeated trauma or tissue scarring, the use of nicotine, inadequate calcium uptake, osteoporosis, an overriding illness, or a restriction in blood supply to the bone resection or wounded area. Several factors can help or hinder the bone healing process. Bone shards can also embed in the adjacent muscle, often causing significant pain.
To promote osseointegration or fusion, surgeons today use a combination of techniques. One method includes introducing healthy bone cells such as those found in the patient's bone marrow into the area surrounding the implant component; however this requires the additional time and consequences of a secondary surgical site. Surgeons also commonly aid bone growth by providing scaffolding in which the bone can grow such as a calcium phosphate ceramic matrix or human bone. As an alternative, a surgeon may use a bone induction material; a material with the capacity of many normal chemicals in the body to stimulate primitive “stem cells” or immature bone cells (osteoblasts) to grow and mature, forming healthy bone tissue, faster than the body normally would. Most of these stimulants are protein molecules called, as a group, “peptide growth factors” or “cytokines”. One group of proteins that has been used to cause osteoinduction is a genetically engineering protein called Bone Morphogenetic Proteins (BMP). However, this is a foreign substance that takes time to work with and may induce bone growth outside on the intended implant site. It has also been known to simulate tissue other than bone to grow.
Aside from BMPs, other growth factors including fibroblast growth factor (FGF), platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-β) may promote the division of osteoprogenitors, and potentially increase osteogenesis. UCB is another human recombinant protein that is currently under development, similar to BMP that helps control bone regeneration, but reportedly without some of the ectopic side-effect.
Referring now to FIG. 1A, an illustration of an exemplary hip joint 100 is shown including a femur bone 110 and pelvic bone 150. An exemplary artificial hip system 120 is partially installed and is shown in an exploded form for better explanation of the figure. Artificial hip system 120 may include an acetabular system 122 and femoral component 124. This illustration is shown with part of the femur and pelvic bone cut away to show resected and prepared areas 112 of the bone. As shown, femur 110 has been prepared to receive femoral component 124, commonly achieved by reaming or resecting the core of femur 110. Exemplary resected areas 112 are indicated. Femoral component 124 and resected femur 110 may be a pressfit together and the femoral component 124 surface may be roughened or treated to promote a stronger bone-to-implant integration. Alternatively, cement (not shown here) or implant coatings may be used to help provide a scaffold and provide for better osseointegration. Acetabular system 122 is formed to fit within a prepared acetablum 148 of the pelvic bone 150 and appropriately shaped resection tools, such as cupped reamers (not shown here) are available to the surgeon to prepare the acetabulum 148. Preparation of the acetabulum 148 may include scraping, cutting or drilling depending on the patient and exemplary resected areas 112 are shown. Acetabular system 122 may be fixed within acetabulum 148 using cement (not shown here) or through a pressfit. Bone screws 125 may be used to provide improved fixation. Acetabular system 122 and/or femoral component 124 may also have a porous coating or sintered surface (not shown here) to improve implant fixation with bone as the bone grows so as to integrate with the implant component. While screws and mechanical mean of fixation are used, bone remodeling so as to at least partially integrate with the implant component preferable to the long term success of the procedure.
Referring now to FIG. 1B, a knee joint 200 is shown, including a femur 205 and tibia 210 with a knee implant system 250 in place. During an implant procedure, femoral distal portion 206 may be resected and a knee femoral component 255 may be assembled as shown. Exemplary resected areas at the femoral distal portion are shown 260. Femoral component 255 may be attached to femoral distal portion 206 with cement or with a press fit, similar to that described in FIG. 1A. In addition tibial proximal portion 211 may also be resected to fit with a tibial knee component 270. Exemplary tibial resected areas 271 are shown. Some but not all tibial resected surfaces 271 are indicated on FIG. 1B. In between femoral component 255 and tibial component 270 a plate 275 may preferably be included. Plate 275 is adapted to allow femoral component 255 to rotate as the knee 200 articulates, with an appropriate feel and resistance, while plate 275 is preferably constructed from a very resilient and low friction material, such as high density polyethylene, reducing the effects of material wear over time. Similar to the hip implant system described earlier, while pressfits, screws, cements and other acute means of implant fixation are used by the surgeon, early and strong osseointegration is often an important factor in achieving a successful procedural outcome.
Referring now to FIG. 1C, an illustration is shown of a shoulder joint 300, including a humerus 310 and the socket portion or glenoid 320 which is part of the scapula 322. An exemplary replacement implant system 350 is shown in the illustration, often required due to pain from arthritis in the shoulder joint 300. The illustration is shown in an exploded form to better demonstrate the implant 350 and resected areas 314. During the procedure, the glenoid socket 320 is reamed or resected and holes 324 may be drilled so as to fit well with the matching shape of the glenoid socket implant 360. Bone screws (not shown here) may be used and inserted into drilled holes 324. The implant 360 may then be press fit into the prepared glenoid socket 320, and similar to previously discussed implants, the implant may have a variety of methods to improve the fixation of the implant. Porous or cancellous bone in the center of the humerus 310 is removed through reaming and general resection and the head of the humerus is removed. The stem implant 370 may then be inserted into the humerus canal and a variety of fixation means may be used, as discussed previously, to keep the stem implant in place and promote osseointegration. The ball implant 312 is then attached to the head of the humerus 310. This ball may be nested within the glenoid implant 360.
Referring now to FIG. 1D, an exploded illustration of a root form dental implant 400 is shown including the jaw bone 410, dental implant system 415 and two natural teeth 425 with teeth roots 420. Dental implant system 415 includes an implant root 430, an implant post 435 and a crown 438. The implant root 430 screws into the jaw bone 410, to fit within the jaw bone 410 similar to a natural tooth root 420. The implant root is typically constructed from titanium and before insertion into the bone 410 a tunnel 450 is typically drilled or resected to prepare the bone 410 to receive the implant root 430.
As with all the implant systems described earlier, in order for this implant system 415 to succeed, the surface of the drilled tunnel 450 and any other surrounding and supporting bone 410 should preferably partially heal, remain healthy, and a portion should osseointegrate with the implant root 430. The patient's body will naturally aid this healing and growth process through the pressure from chewing on the implant crown 438 transmitting to the underlying bone 410. However, the dental patient may not always have healthy underlying jaw bone 410 due to previous extractions, injuries, cysts or infections. Jaw bone grafting or jaw bone augmentation may be needed to supplement the implant procedure and improve procedural outcome. There are also other dental implant system designs that require less jaw bone 410, not described here, including blade implants that have a narrower root region for areas of reduced jaw bone. Alternatively a method of augmenting the existing jaw bone may be used.
FIG. 1E shows an illustration of an exemplary fractured bone 505 with a plate system attached 500, shown in exploded form to better demonstrate the resected areas. An exemplary bone fracture 510 is shown with a plate 550 and bone screws 555 assembled to secure plate 550. This plate 550 is intended to help maintain the bone 500 and fracture 510 in the correct position and support the bone as the fracture 510 heals. There are many forms of bone fracture in many areas of the body with a variety of bone plates, support structures and screws that may be used in a similar fashion with a similar intent, to the one described above.
Plate 550 may be attached to bone 500 through drilled bone tunnels 560 prepared to receive at least one bone screw 555. Bone screws 555 may be used in conjunction with cement to improve the interface strength between the bone 500 and screw 555. Assuming plate 550 and bone screws 555 are intended to be permanent fixtures in the patient, the long-term success of this medical procedure will significantly impacted by the ability of the fractured bone 510 to heal and the plate 550 and screws 555 to maintain a strong bond or osseointegrate with the surrounding bone areas, such as drilled surfaces 561 and prepared outer bone surface 551. Outer bone surface 551 may be prepared to receive the plate 550 so as to form a better mating surface with the plate and help augment the implant-to-bone fusion process. Fracture 510 may also be cleaned of debris, if the fracture is accessible.
FIG. 1F illustrates an example of an autogenous bone grafting harvest, where an autogenous bone graft 605 may be taken from a harvest site 600, leaving exposed bone surfaces 630. Here an exemplary site is a patient's iliac crest 610, although other areas are also used such as the mandibular symphysis (chin area), fibula or ribs. The bone graft 605 may then be utilized in a patient' spine or jaw, a bone fracture site or any other area to provide bone producing cells and scaffolding to assist in the healing and bone growth. Thereafter, two areas exist where bone needs to heal and grow. In this example, the graft 605 itself as well as the harvest site resected area 630. The area of harvest is often problematic post surgery, associated with high donor morbidity and it can be the source of significant pain, often more than the pain from the primary surgical site. Over time, the exposed area 630 is expected to heal, remodel and fuse back together, which does not always happen reliably.
Additionally, there are many other bone implants and portions of bone not described here in detail where bone repair and remodeling is preferable. These include, but are not limited to soft tissue anchors, ligament graft anchors or screws within a bone tunnel, elbow and hand implants, spinal implants and bone fractures throughout the body.
FIG. 1G shows an exploded illustration of a dental crown or cap 650. Crown 650 is often used to repair a fractured or weakened tooth that can no longer receive a dental filling. Typically the original tooth 660 is shaped and made smooth and any plaque or decayed tooth in removed, so as to receive the crown 650, using a variety of dental tools such as a dremel or drill. Exemplary prepared surfaces 655 are shown. Cap 650 may have been prepared earlier to match the patient's bite and size requirements and may be slipped over the tooth 660 and cement or a fixative (not shown here) may be used to keep the crown in place. Cap 650 is usually made from a metal alloy, porcelain or dental ceramic. Since teeth do not grow or remodel, this fixative is expected to retain the crown 650 in position for the lifetime of the cap 650. Therefore a great deal of attention is paid to the tooth surface 655 to ensure it is clean and sterile to maximize the connection strength and reduce any likelihood of infection, in the area between the crown 650 and tooth 660 over time.
Accordingly, there remains a need for new and improved methods for use in preparation for hard body tissues to receive an implant. In the case of bone tissue a need for a new and improved method to preferably promote the repair and subsequent bone growth is needed to address certain of difficulties aforementioned. It is therefore an objective to provide methods and systems to facilitate these goals.